AD-AIOS 698 OKLAHOMA STATE UNIV STILLWATER FLUID POWER RESEARCH -ETC F/6 13/7HYDRAUL IC SYSTEM ACOUSTICAL DIAGNOSTICS. 1U)DEC 80 Rt INOUE, Rt K KING OAAK7n-79-C-0139

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I Report No. FPRC 80-A-Fl

HYDRAULIC SYSTEM ACOUSTICAL DIAGNOSTICS

FINAL REPORT

DECEMBER, 1980

PREPARED FOR

U.S. ARMY MOBILITY EQUIPMENT RESEARCHAND DEVELOPMENT COMM4AND

FORT BELVOIR, VIRGINIA 22060

1( PREPARED BY DTICPERSONNEL OF THE

D TFLUID POWER RESEARCH CENTER ELECT TOKLAHOMA STATE UNIVERSITY DEC I 8

STILLWATER, OKLAHOMA

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CONTRACT NUMBER

DAAK70-79-C-0139 Is dmmt has ban OPPO I

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REPORT DOCUMENTATION PACE RF!4D INZ: rIcI IONS- -_____ -- lE FORE OMPLETING FORM

F-F~ ~ d ~ . )VI A-. I-S!,ON N01 I Q--F-PIFN frt. (7ATA,.OG WLJMaEN

FPC80-A-Fl _____

Final Technical Paper

Hydraulic System Acoustical Diagnostics September, 1979, Aug. 1980

- _______

t IdiFM~S~ i Td.

Staff of the Fluid Power Research Center i DAAK70-79-C-0139

P. kEPONN Of--7A1F.ZAT40N NMt Aj TAODRESS Y, T ~ No -A-, SFluid Power Research Center ''.AF NUR'

Oklahoma State UniversityiStillwater, OK 74078

II~ ~ ~ b ity quipment Research and jDcme_____. eebr1980 ____Development Commuand, Procurement and Productionr

Office, Fort Belvoir, VA 22060 _

.vv(,NI'ON;N' AF.. N(-Y NAME -% ADDRF$S(iI dlffo-,nt Ir-, CntlOffrt. L .

ONRRP, Room 582 Federal Bldg. FUnclassified

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APPROVED FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED

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19 '7- -WOFFOS (Continue on Freerve sido, It nr'ceavary anti Idei~rfy hv hlncok orTjm-er,

Acoustical Diagnostics Non-Intrusive DiagnosticsCavitation Fluid Power DiagnosticsWear Hydraulic Vane PumpBearing Damage

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ABSRACT

This project is a continuation of previous acoustics studies con-ducted a*-t-Rtid--Pewer Research- Center to determine if the vibrationsignature of hydraulic components could provide information concerningthe operational health of the system. The concept of using internallyproduced noise to detect incipient failure is not new (the screwdriver-to-the-block trick used by automobile mechanics is a good example);however, the technique has been more of an art than a science, espe-cially where hydraulic systems are concerned.

This study advances the previous work by applying the concept tovane pumps into which specific known degradation has been introduced.The study showed that, by using case-mounted accelerometers, signifi-cant vibratory differences can be detected and associated with givenconditions.

I

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SUMMARY

The application of non-intrusive diagnostic techniques to determine

the internal health of hydraulic systems would provide hydraulic equip-

ment users with an important maintenance tool.

Two diagnostic methods, one using microphones to detect airborne

noise and the other using accelerometers to detect structureborne noise,

were considered. The structureborne noise was found to be a more feasible

field diagnostic method to detect failures on hydraulic components than

the microphone.

By using an accelerometer mounted on the test vane pumps, detection

of such malfunctions as cavitation, severe internal wear, and bearing

damage was demonstrated.

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PREFACE

This report is the Final Technical Report for the Hydraulic System

Acoustical Diagnostics project, Contract DAAK7O-79-C-0139. This report

documents both the theoretical and experimental aspects of diagnosing

hydraulic vane pump degradation acoustically.

This study was conducted by the staff of the Fluid Power Research

Center, Oklahoma State University, directed by Dr. E. C. Fitch, Jr. Mr.

Riichi Inoue, and Mr. R. K. King were the Principal Investigators and Mr.

Don Stremme was Project Engineer. Dr. Richard Lowery of the School of

Mechanical and Aerospace Engineering of Oklahoma State University pro-

vided invaluable technical assistance as a Faculty Associate.

Project personnel contributing major efforts to the project were:

A. Nipper

K. Stokes

J. Bruce

C. Totty

In addition, various members of the Fluid Power Research Center staff con-

tributed to this study.p.

The Contract Officer Technical Representatives for this contract

were Mr. James Dillon and Mr. Delmar Craft.

L

The contract was monitored by the U.S. Amy Mobility Equipment

Research and Development Command, Fort Belvoir, Virginia.

[

TABLE OF CONTENTS

CHAPTER PAGE

I Introduction ..... ............... 1

II Technical Background .... ........... 2

III Evaluation of Transducers inDiagnostic Method .... ............. 6

* Microphone Method .... ........... 6* Accelerometer Method .............. 8* Experimental Test .. ........... 10* Test Data Interpretation. ........ 17* Transducer Evaluation ... ......... 22

IV Acoustical Diagnostic Test ... ........ 24

* Test Procedure ................. 24* Test Facility .... ............. 28* Data Analysis Procedure ... ........ 29

V Test Results and Analysis ............ 33

* Cavitation ..... ............... 33* Wear ...... .................. 38* Damaged Bearing .............. ... 42* Result Summary ................. 46* Further Investigation ........... .. 47

VI Conclusions and Recommendations ........ 51

REFERENCES . . ... .. ........................ .. 53

APPENDIX

A Details of Pump Break-In ........... 54

B Diagnostic Test Procedures ... ........ 59

C Test Facility .................. ... 61 i

D Test Stand Controller ............... 70

4.. ,-

LIST OF TABLES

TABLES PAGE

3-1 Transducer Limitations .... ........... 22

5-1 Test Result Summary ................. 46

LIST OF FIGURES

FIGURE PAGE

2-1 Non-Intrusive Diagnostic System .......... 3

2-2 Diagnostic System for Field Application ... 4

3-1 Piezoelectric Accelerometer Construction . . 9

3-2 A Typical Vibration Measurement System . . . 11

3-3 Vane Pump Frequency Spectrum byAccelerometer in Normal Operation ........ 12

3-4 Vane Pump Frequency Spectrum byMicrophone in Normal Operation ... ....... 14

3-5 Vane Pump Frequency Spectrum byAccelerometer in Cavitation ............. 15

3-6 Vane Pump Frequency Spectrum byMicrophone in Cavitation ............ ... 16

3-7 Vane Pump Frequency Spectrum byAccelerometer with Vane Damage ... ....... 18

3-8 Vane Pump Frequency Spectrum byMicrophone with Vane Damage ............ 19

3-9 Changes of Harmonic Frequency AmplitudesDue to Failures by Accelerometer ........ 20

3-10 Changes of Harmonic Frequency AmplitudesDue to Failures by Microphone ........... 21

4-1 Time-Frequency Spectrum ............... 26

-ALA- k: o l;

LIST OF FIGURES

FIGURE PAGE

5-1 Cavitation Vibration Amplitude vsHarmonic Order ..... ................ 35

5-2 Cavitation Baseline Difference vsHarmonic Order ..... ................ 36

5-3 Cavitation Signature Difference vsHarmonic Order ..... ................ 37

5-4 Wear Vibration Amplitude vsHarmonic Order ..... ................ 39

5-5 Wear Baseline Difference vsHarmonic Order ..... ................ 40

5-6 Wear Signature Difference vsHarmonic Order ..... ................ 41

5-7 Bearing Damage Vibration Amplitude vsHarmonic Order ..... ................ 43

5-8 Bearing Damage Baseline Difference vsHarmonic Order ..... ................ 44

5-9 Bearing Damage Signature Difference vsHarmonic Order ..... ................ 45

5-10 Vane Pump Frequency Spectrum ............. 485-11 Vane Pump Frequency Spectrum--Translated. . . 48

5-12 Logic Chart .... ................. ... 50

A-1 Non-Intrusive DiagnosticsBreak-In Procedure .................. .. 56

A-2 Ferrographic Analysis in Pump Break-In. . . . 57

C-I Test Facility .... ................ .. 62

C-2a Aeration Control Test Stand ... ......... 63

C-2b Fluid Conditioning Stand .............. 64C-3 Air Injecting and Mixing Vessel ... ....... 64

.. .. I .___._____._.: - . .

LIST OF FIGURES

FIGURE PAGE

C-4 Typical Pump Contaminant SensitivityTest Circuit ..................... ... 67

C-5 Pump Operation in the Reverberent Room .... 68

D-1 Instrumentation System .... ............ 71

D-2 Microcomputer Test Control System ..... ... 75

D-3 Test Analysis System ................. 76

4 .-

CHAPTER I

INTRODUCTION

Most of the current diagnostic techniques to detect or predict

failures of the fluid power system require shut-down of the system oper-

ation. A non-intrusive technique is desirable which would allow com-

ponent performance analysis to be performed with no down time.

In the process of transmitting energy by means of fluid, some energy

is dissipated as vibration and acoustical noise. As the performance of

a component degrades, more energy is emitted as a result of the component's

decreased efficiency. Hence, machine performance degradation can possibly

be monitored by measuring vibration and noise.

This document is the final report of the first phase of a project

to determine if distinctive, repeatable signals can be obtained to show

that such a monitoring technique is feasible. To investigate this fea-

sibility, two diagnostic methods were evaluated in conjunction with the

signals generated by vane pumps: one using a microphone to measure

airborne noise and the other using an accelerometer to monitor vibration.

Experimental test data obtained by the two methods are presented, and the

comparative diagnostic capabilities of the methods are discussed.

* I - __

I *

aftI .

1 CHAPTER II

TECHNICAL BACKGROUND

The goal of the project was to develop a potential non-intrusive

diagnostic technique which could be packaged into a dedicated field

system. The concept of a non-intrusive diagnostics system can be sim-

plified into three phases as illustrated in Fig. 2-1.

Transduction is associated with the conversion of a desired meas-

urand into an equivalent electrical waveform. In this study, the meas-

urand is airborne and structureborne noise emission, the corresponding

transducers being microphones and accelerometers, respectively.

Data processing consists of digitizing the electrical waveform

and processing the data in the desired format. Through this process,

the incoming signature from the transducer would be averaged and reduced

to the desired format by a Fourier analysis or other analytical proce-

dures. The data are then presented in the desired format for analysis.

Once the data have been analyzed, an evaluation of machine condition can

be achieved by a preprogrammed microcomputer.

The hardware of diagnostic systems consists of transducers and a

microprocessor to transform the data into the desired format and to

proceed through the necessary data reduction. Fig. 2-2 illustrates the

possible extent of a diagnostic system and was used as a guide through-

out the project. The figure proposed three different systems that

2

_______ _________________________9A___

TRANSDUCTION]

DATA PROCESSINAND ANALYSIS

DECISIONCOMPONENT EVALUATION

FIG. 2-1. Non-Intrusive Diagnostic System

.4

TYRANSUCSE SYDNATURE---OMNALYZE

0I0612a

FIG. 2b NLYE

FIG. 2b

FIG. 2-2. Diagnostic System for Field Application

4

could be utilized. Fig. 2-2a illustrates a complete portable field unit,

in which the transducer is temporarily placed on the component under test

and analyzed by a portable noise signature analyzer. Fig. 2-2b illus-

trates the concept of having the transducers as a permanent installation

of the hydraulic system. The portable analyzer is connected to a central

unit which connects the analyzer to various components. Fig. 2-2c repre-

sents a much more elaborate system in which both the transducers and the

analyzer are permanently installed on the system. Fig. 2-2c, although

more expensive than others, offers the advantage of utilizing a micro-

processor that can be used for other control systems on the hydraulic

machine. Another distinction in the method illustrated in Fig. 2-2c is

it proposes that the analysis of the component be exclusive of human

interface. This eliminates the chance of misinterpretation. Two types

of transducers are available for the diagnostic system; a piezoelectric

accelerometer and a microphone. The piezoelectric accelerometer, due to

its ruggedness, could be utilized in all three proposed systems, while

the microphone would be applicable in Fig. 2-2a only.

5

CHAPTER III

EVALUATION OF TRANSDUCERS IN DIAGNOSTIC METHOD

The initial phase of the project began by choosing the method of

transduction to be utilized for the development of a non-intrusive diag-

nostic technique. Microphones and accelerometers were evaluated. Both

methods are currently being utilized in the area of machinery diagnos-

tics. The transducer methods were compared on the basis of experimental

performance and compatibility with field environments.

The energy dissipated by a component in the form of vibration pro-

vides information relating to its operating condition. The vibration

of a hydraulic pump is the result of the energy conversion process

(mechanical and hydraulic) in addition to the mechanical impact that

takes place during the pump's operation. Flow production and mechanical

interactions transmit energy in the form of vibration throughout the

pump's housing. The vibratory action of the pump housing produces air

pulsations or soundwaves which constitute the airborne emissions of the

pump. It has been experimentally verified that the vibration characteri-

stics of an operating pump can provide information concerning the operating

integrity of the component. The transducers were chosen to measure the

vibration characteristics of the pump in its two forms--airborne noise

(microphone) and structureborne noise (accelerometer).

MICROPHONE METHOD

Any object that vibrates will generate sound due to the movement

6

of air in the vicinity of the object. The simplest form of noise source

is a sphere that vibrates uniformly over its entire surface. This source

radiates sound in all directions from its geometric center. It then may

be considered as a "point" source insofar as radiated sound is concerned.

If this source is far from any other source, then the sound field

produced is called the free field. As a rule of thumab, a microphone is

said to be in the free field when its distance from the source is greater

than one wavelength of the lowest frequency to be measured.

The free field condition does not occur in practice because sound

is reflected from nearby objects such as floors, walls, and ceilings.

This phenomenon can be controlled in the laboratory environment, but

controlling the field environment is virtually impossible; however, if

one is concerned only with changes in a signature rather than an abso-

lute noise signature, the free sound field is not necessary. Such is

the case when diagnosing changes in the performance of fluid power cam-

ponents. Therefore, the microphone data are obtained with the transducer

positioned in the near sound field or "near field." A microphone is said

to be in the near field when the distance from the transducer to the

noise source is no greater than one wavelength of the lowest frequency

to be measured, and preferably much less.

The purpose of near field noise measurements is to isolate the

microphone from any background noise. When testing a fluid power pump,

7

* . * I'

the microphone should "see" only the pump noise, and it should be blind

to noise from piping, valves, drive shafts, and so forth. Thereforth,

the microphone should be placed very close to the pump's surface. The

microphone position for the purposes of this project was 4 mm from the

pump's surface, centered on the vane rotor housing.

ACCELEROMETER METHOD

The use of vibration signature analysis is a logical choice, since

it involves mechanical events such as impact, rolling, and sliding actions

inherent in rotating machinery. The waveform of the vibration of a com-

ponent contains a great deal of diagnostic information. For example, the

timing of events with respect to each other may be of importance. In

addition, the presence or absence of particular noises indicative of

mechanical events is important when evaluating component performance.

Vibration levels are usually monitored with transducers called accel-

erometers. These are mounted rigidly to the test component and produce

a voltage proportional to the acceleration of the component structure.

There are several types of accelerometers available, but the piezoelectric

is the most common. These transducers have large output-voltage signals

and are available with very high natural frequencies. Typical construction

of piezoelectric accelerometer is shown in Fig. 3-1.

In most measurement systems, the accelerometer is used in conjunction

with a high-impendance charge amplifier to obtain accurate low-frequency

8

CAP

HEMISPHERICAL~SPRING

MCRYSTAL

USED INCOMPRESSIONMETALLIC CASE

-SERVES ASONE OF THEELECTRODES

AND LEAD WIRES

LEAD WIRE ATTACHED TOUPPER PLATED SURFACEOF CRYSTAL

FIG. 3-1. Piezoelectric Accelerometer Construction

., I

response. Furthermore, charge amplifiers are relatively insensitive to

cable capacitance which is essential when long transmission cables are

used. A typical vibration measurement system is shown in Fig. 3-2.

Size selection of an accelerometer is important since a large

accelerometer mounted on a small component will alter the component's

dynamic characteristics. These transducers are available in a wide

variety of sizes; however, there are trade-offs to be considered. As

a rule, small accelerometers are less sensitive than larger ones but

have higher resonant frequencies, which is often desirable.

EXPERIMENTAL COMPARISON TEST

Two fluid power vane pumps were tested which were of the same

manufacturer's series with the same displacement. Each pump has 12

vanes that divide the flow into discrete volumes. The pumps were driven

at 1200 rpm. A peak is expected when each vane passes by the transducer.

Since there are 12 vanes, the fundamental vane passage frequency is 240 Hz.

The first few harmonics of the fundamental frequency spectrum can

be observed on the frequency spectrum graph. If the fundamental frequency

is given by f(o), then the first harmonic is 2f(o), the second is 3f(o),

and so on. This gives us the first harmonic at 480 Hz, the second at

720 Hz, and third at 960 Hz. Higher order harmonics can also be seen,

Fig. 3-3. Note that the harmonics shift around somewhat. This can be

attributed to the fluctuations in the V-belt drive. The data in Fig. 3-3

10

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0 -0)

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...............

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CL z

zoo,

RELATIVE AMPLITUDE

o FUNDAMENTAL

CCI 1st HARMONIC_

0 2nd HARMONIC

0

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0-4-

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12

were obtained with a BBN 507 accelerometer mounted on vane rotor housing.

A charge pump was installed in the inlet line to keep the pump inlet pres-

sure positive, thereby eliminating cavitation. Microphone data are pres-

ented in Fig. 3-4 with no change in pump operation. It is obvious that

the vane passage harmonics are not nearly as clear in Fig. 3-3, but they

do appear. Tests corresponding with Figs. 3-3 and 3-4 were conducted

with the pump operation conditions in Appendix B.

Cavitation data recorded with the accelerometer and microphone are

shown in Figs. 3-5 and 3-6, respectively. To obtain cavitation, the

charge pump was removed from the inlet side of the pump, and inlet pres-

sure was lowered by throttling the line. Otherwise, the operating param-

eters are identical to those in the previous tests. The vane passage

fundamental frequency with its first few harmonics can again be seen.

The accelerometer data in Fig. 3-5 contain hamonics up to the sixth.

While the higher order harmonics do not coincide exactly with the

appropriate multiple of the fundamental frequency, this is to be expected

in a V-belt drive system. The important point is that the microphone data

in Fig. 3-6 also contain the higher order harmonics but they are covered

up by "noise".

The final test involved vane damage similar to that which could

occur in the field. The pump was disassembled and a small groove was

made with a file on the wiping edge of a single vane. The pump was then

installed in the system with other operating parameters remaining un-

changed. In order to simulate vane damage only, the charge pump was

13 II

* ,*-* .*

RELATIVE AMPLITUDE

00--

M0o 3rds HARMONIC-

0

mo

0- 4~. 0

0

0

4r 0

0

14,

0 4-

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RELATIVE AMPLITUDE

0~ XFUNDAMENTAL

X 1st HARMONIC0

X 3rd

40

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CD

0

0-

01

reinstalled in the pump inlet line. Figs. 3-7 and 3-8 represent acceler-

ometer and microphone data, respectively, for induced vane damage.

TEST DATA INTERPRETATION

From the test data shown in Figs. 3-3 to 3-8, it is obvious that

the frequency spectra change when degradation occurs. The change of

amplitudes at fundamental and harmonic frequencies of the frequency spec-

tra are summarized in Figs. 3-9 and 3-10. Fig. 3-9 shows the change

of amplitudes due to cavitation and vane damage as monitored by an

accelerometer. Cavitation decreases only the second and the third

harmonic amplitudes significantly, while vane damage decreases all

fundamental, first, second, and third harmonic amplitudes down to 40

percent of the original values.

Fig. 3-10 shows the change of amplitudes as monitored by microphone.

Cavitation decreases fundamental and second harmonic amplitudes signif-

icantly; whereas, vane damage decreases fundamental, first, and second

harmonic amplitudes.

The above observation proves the possibility that failures can be

detected and identified by monitoring the frequency spectra; however,

it should be noted that the accelerometer method has failure detection

criteria which are different from the microphone method. This is due

to the fact that the former measures structureborne vibration while the

latter measures airborne noise.

17

M.A -16 Mt

RELATIVE AMPLITUDE~gir

0 X FUNDAMENTAL

rD 0

X 1st HARMONIC00 X 2ndco

m 0 X 3rdmo0

0*

C, 0ID X(D N _

-3m C+ 0CD

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*- NORMAL CONDITION*-U IN CAVITATIONA-A VANE DAMAGE

1.0 _ _ --

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w

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FUNDAMENTAL 1st 2nd 3rd

HARMONICS

FIG. 3-9, Changes of Harmonic Frequency AmplitudesDue to Failures (Accelerometer)

20

~~NORMAL CONDITION*-4 IN CAVITATION

A-A VANE DAMAGE

0

0.6-

20.4-

FUNDAMENTAL 1st 2nd 3rd

HARMONICS

FIG. 3-10. Changes of Harmonic Frequency Amplitudes

Due to Failures (Microphone)

21

TRANSDUCER EVALUATION

Although the two diagnostic transducers, the microphone, and the

accelerometer were found to be capable of detecting failures of

hydraulic components, the failure criteria when using the microphone

are different from those using the accelerometer. The criteria with

the accelerometer are more consistent from a decision-making stand-

point because the abnormal amplitude ratios are always less than the

normal ones; whereas, the abnormal amplitude ratios with the micro-

phone are either less or more than the normal ones.

Another important aspect to be considered as a field diagnostic

transducer is a degree of environmental limitations. The limitations

of each transducer are presented in Table 3-1. Each transducer has a

Table 3-1. Transducer Limitations

Item of Microphone AccelerometerLimitation

Sensitivity Sensitivity to source Cross-axis sensitivityDirectivity

Influence Reflections and in- Mass loading; influencefluence of microphones of the accelerometer onpresent on the measure- the vibration of thement surface which it is

measuring

Environmental A. Temperature A. Temperature GradientSensitivity B. Humidity B. Humidity

C. Moisture Condensation C. Sound PressureD. VibrationE. Wind - "Wind Noise"

22

certain limitation corresponding to environmental effects. However,

the accelerometer, because of its enclosed construction, can withstand

a more extreme field environment.

The limitations expressed in Table 3-1 can be compensated in the

laboratory, but the environmental sensitivity is a handicap for the

microphone in the field application. The ruggedness of the acceler-

ometer lends itself the potential to be installed as a permanent part

of a hydraulic system as proposed in Figs. 2-2a and 2-2b.

From the above considerations, it was decided to use the acceler-

ometer to demonstrate and verify the acoustical diagnostic method with

experimental tests.

23

- - -- - -!* _ _

CHAPTER IV

ACOUSTICAL DIAGNOSTIC TESTS

TEST PROCEDURE

Before the tests pumps were subjected to the diagnostic tests,

the pump break-in was achieved. The pump break-in procedure followed

the manufacturer's specifications. Details of the break-in can be found

in Appendix A. The pumps were operated under normal operating conditions

and the corresponding baseline signature was recorded. The baseline

signature corresponds to the frequency spectrum of the undamaged component

under specified operating conditions of speed, pressure and temperature.

The pump would be subjected to abnormal operating conditions of wear,

cavitation, and damaged bearing with the corresponding frequency spectrum

being analyzed.

The data processed through a spectrum analyzer and the amplitude

(Af) corresponding to the fundamental and harmonic frequencies were

recorded. The diagnostic test procedures and operating conditions can

be found in Appendix B. Pump-mounted accelerometers were used in all

tests discussed in the remainder of this report.

The test procedure used during the project was based on a diagnostic

method which could be used in a field diagnostic unit. The diagnostic

method pertains to processing of the input signature from the transducer

and presenting the data in the desired format for analysis.

24

7

S"

A real time spectrum analyzer was used during the project. The

analyzer received the analog signal from the accelerometer and converted

the electrical waveform into a time and frequency representation. Both

the time and frequency domain are illustrated in Fig. 4-1.

The figure represents the time and frequency display of the vibration

signature from a hydraulic vane pump as seen on the CRT of the spectrum

analyzer.

The upper graticule represents the time domain signature of the

vibration which shows the vibration amplitude versus time. The lower

graticule is a display of the same signal in the frequency domain;

amplitude versus frequency. The time domain analysis is a very effective

method for qualitative analysis of an incoming waveform. The frequency

domain is a quantitative analysis of how the energy within the waveform

is dispersed versus frequency.

The diagnostic method will utilize the frequency domain analysis

which also is referred to as spectrum analysis.

The frequency range of investigation must be selected prior to

transducer selection. The frequency range will depend on the components

under investigation. The project tested hydraulic vane pumps which were

of the same manufacturers' series with the same displacement. Each pump

has 12 vanes which divide the flow into discrete volumes. The pumps were

25

IJ

mm MN

C#) m010

20

m zN

D

m- -

> --

26

driven at 1200 rpm (20 Hz). A peak is expected in the pump frequency

spectrum when a vane passes by the transducer. Since there are 12 vanes

in the test pumps, the fundamental frequency or vane pass frequency is

240 Hz. If the fundamental frequency is given by fo, then the first

harmonic is 2fo, third 3fo and so on. The analysis of the vane pump

operating at 1200 rpm set the frequency range of investigation 0-1680 Hz

to include the first seven harmonics. Therefore, accelerometers were

selected to detail the frequency range of 0-2 kHz.

The signal averaging techniques applied to the input signal is an

important characteristic of the diagnostic method. A real time spectrum

analyzer was utilized throughout the project. "Real time" refers to the

analysis capability of processing and sorting the incoming analog signal

faster than it is being received by the analyzer. Inherent in real time

analyzers is the processing capability of signal averaging. Signal

averaging techniques reduce the noise content of the input signature and

enhance the appearance of periodicities within the frequency spectrum.

Signal averaging is an important parameter in the diagnostic method util-

ized in spectrum analysis of rotating components, such as hydraulic pumps

and motors, due to its enhancement effect on the amplitudes of the peri-

odic fundamental and corresponding harmonic components in the signature.

The display characteristics of the frequency spectrum relate to the

characteristics of the waveform which are to be analyzed. This project

utilized the root mean square (RMS) value of the waveform for analysis.

27

I

The RMS values can be summed on an energy basis to give an overall RMS

value for a range of frequencies, or they can be used to give the ampli-

tude of various frequency components. Analysis of the RMS value of the

frequency spectrum combined with proper averaging techniques results in

the most repeatable format for analyzing and comparing data. The analysis

technique may vary corresponding to the test under investigation.

Obtaining a peak hold spectrum may be applied where the highest am-

plitude for each frequency component of the spectra is maintained, result-

ing in a spectrum of maximum values. This method may be applied to anal-

ysis of transient behavior as in cavitation; however, in conjunction, an

RMS analysis should be made.

The diagnostic method utilized in the project for evaluating hydrau-

lic vane pumps consisted of evaluating the RMS amplitudes of the funda-

mental and corresponding harmonic frequencies of the vane pass frequency.

The averaging time was held constant corresponding to the necessary aver-

ages for the spectrum to remain stationary; whereas, the amplitude density

distribution did not vary with time.

Facility

The test facility provided control of the various operating param-

eters on the component under test. It also provided the capability of

collection and processing of the vibration signatures emitted from the

test components.

28

41.

L ,

The fluid conditioning test stand was constructed to control inlet

pressure, outlet pressure, fluid temperature, pump speed, and fluid

aeration level. Details of the test facility are in Appendix C.

The project promoted the development of a microprocessor test stand

controller. The advantage of the controller was twofold. First, to

monitor the test parameters to their preset values and, second, to

initiate the development of a microprocessor for signature analysis

which would be applicable in the field. Detailed descriptions of the

controller and the instrumentation utilized in the project are in Appendix

D.

Data Analysis Procedure

The amplitudes were analyzed for each abnormal operating mode of the

pump. Two analysis methods were investigated for implementation as a

diagnostic evaluation method. The baseline difference (BD) is defined

by Eq. (1)

BD = AfB - AfH (1)

Where: AfB = the vibration amplitude corresponding to specified hamonic

frequency in the baseline signature.

AfH = vibration amplitude corresponding to a specified harmonic

frequency relating to an abnormal operating condition.

The baseline difference is a diagnostic method in which the differ-

ence in amplitudes of the harmonic frequencies between the baseline

29

* *.;* *

signature and a signature representing the pump's present operating con-

dition are compared. The other diagnostic method utilized is the sig-

nature difference (SD) as defined by Eq. (2).

SD = Afo - AfH (2)

Where: Afo vibration amplitude corresponding the hydraulic component0

fundamental frequency relating to an abnormal operating

condition.

A = vibration amplitude corresponding to a specified harmonic

component of the fundamental frequency relating to an ab-

normal operating condition.

The signature difference is a relationship between the difference

in amplitude between the vibration signature fundamental and corresponding

harmonic frequencies.

The primary difference between the baseline difference and signa-

ture difference methods is in the number of acoustic traces necessary for

the analysis. The baseline difference technique is based on the relation-

ship between a permanent record of the acoustic signature of the pump

when it is first put into operation (supposedly in a healthy state) and

the signature of the operational (and perhaps degraded) pump. For field

application, this would require the permanent storage and availability of

the baseline signature of each pump.

The signature difference method, on the other hand, is based solely

30

• 1 .I. . ... 1 " :- . .

on the relative amplitudes of the fundamental and corresponding harmonic

components of the operating pump.

It must be noted that the proposed methods of analysis relate to

a diagnostic method for rotating hydraulic components such as pumps and

motors. The relationships analyze the amplitudes from ti.3 harmonic com-

ponents of a frequency spectrum which can be attributed to a periodic

input signal. Only rotating hydraulic equipment produces periodic

characteristics in its resulting frequency spectrum. The analysis method

used would not be applicable in diagnosing the operating condition of

valves, for it does not possess periodic characteristics in its mechan-

ical operation. It is proposed that a complete diagnostic unit, analyz-

ing various components of a hydraulic system, would include a combination

of diagnostic methods which will have been developed for each type of

hydraulic component. The variations would consist of different frequency

ranges, averaging techniques, and the characteristics of the input wave

form that are to be analyzed; i.e. peak to peak, RMS, power spectral

density.

The next section discusses the results in applying the two methods

to operating conditions of cavitation, wear, and bearing damage utilizing

accelerometer transduction. The plan of attack of the testing procedures

were as follows:

1. Record the vibration signature corresponding to the baseline and

31

abnormal operating conditions of wear, cavitation, and damaged

bearing.

2. Analyze the resulting frequency spectrum, the baseline difference,

and signature difference analysis methods.

3. Evaluate the diagnostic methods for qualitative information con-

cerning the feasibility of utilizing accelerometers as a non-

intrusive diagnostic tool for application in hydraulic systems.

32

-.

CHAPTER V

TEST RESULTS AND ANALYSIS

This section discusses the test results and analysis of vibration

signatures corresponding to abnormal operating conditions. The acousti-

cal signatures will be analyzed corresponding to three levels of severity

of cavitation, wear, and damaged bearing. Both the baseline difference

and signature difference will be presented for comparison of the two

methods.

Cavitation

Cavitation is an undesirable operating condition for any hydraulic

system. Cavitation of a hydraulic pump can not only decrease its oper-

ating efficiency but, through prolonged operation, can physically damage

the pump. The potential for incipient failure of a hydraulic component

due to cavitation leads to the desirability of its early detection.

The pump was subjected to three degrees of severity of cavitation.

The first degree of cavitation severity was defined as a slight cavitation

which can hardly be heard by human ears. The second degree was a cavi-

tation which can be heard by human ears if attention is directed to it.

The third degree was a heavy cavitation which can be readily heard without

attention. The degree of cavitation was controlled by two parameters;

pump inlet pressure and the fluid aeration level. The pump inlet pres-

sure was used as a catalyst to increase the bubble formation in the fluid

33

..

at the inlet of the pump. As the inlet pressure was decreased, the sever-

ity of cavitation increased accordingly, due to the increase in air bub-

bles entering the pumping chamber. The aeration level acts as a "sink"

from which the air bubbles form. The control of the aeration level was

to enhance the repeatability of the severity levels throughout the cavi-

tation test.

Fig. 5-I is a representation of the vibration signature for the

first seven harmonics resulting from the three different severity levels

of cavitation. The figure shows an actual decrease in the vibration ampli-

tude throughout the first level of severity. This indicated that the

inlet pressure at the first degree of severity is above the incipient

pressure corresponding to the operating conditions of the pump.

Incipient pressure is defined as the pressure at which the release

of entrained air cushions the effect of the resulting cavitation. Maroney

(2] found similar results from cavitation tests where the sound pressure

level of a hydraulic gear pump actually decreased as the cavitation level

increased until it reached an incipient pressure.

The analysis methods applied to the cavitation situation are shown

in Figs. 5-2 and 5-3. Fig. 5-2 shows the baseline difference analysis,

and Fig. 5-3 shows the signature difference analysis. For the detection

of cavitation situation, the baseline difference, Fig. 5-2, lacks con-

sistency; however, the signature difference analysis offers a clear

34

I,.... I ° : r . '

• , L ' ;,,

0-

* BASELINE* 1st DEGREE

-W 2nd DEGREE-10- -0 3rd DEGREE

.0

2 -

0.00 00

00

Lo-40->S

-50-

-601 2 3 45 6 7

HARMONIC ORDER (V,,

FIG. 5-1. Cavitation -Vibration Amplitude vs Harmonic Order

35

251 0 1 st DEGREE

* 2nd40-3rd

Z 20-

0

z 15-

LL

z

0

0 00

1 2 3 4 5 6 7HARMONIC ORDER N)

FIG. 5-2. Cavitation Baseline Difference vs Harmonic Order

36

35~ 0 ?SELINE

-o 2nd0-3rd

30-

25 0

0

w 40o 20zwwU- 0

o) 15w

F-z 0S2lo-co0

5

10 1 2 3 4 5 6 7

HARMONIC ORDER (fH&

FIG. 5-3. Cavitation Signature Difference vs Harmonic Order

37

tendency for cavitation severity. The signature differences above the

fifth harmonic show the severity. Especially, the signature difference

at the sixth harmonic distinguishes the cavitation severity clearly.

Wear

Wear is a common replacement criterion for hydraulic components.

The flow degradation associated with a worn hydraulic pump severely de-

creases the efficiency of the entire hydraulic system. The degradation

associated with a worn pump can be related to decrease in volumetric

efficiency, which in turn can be attributed to the increased leakage

paths and clearances associated with internally worn parts.

Theoretically, the wear (in this case intentionally induced by run-

ning the pump with fluid contaminated with AC Fine Test Dust) should alter

the vibration signature of the pump. The tests were to analyze whether

these changes could be detected by conventional accelerometers.

Fig. 5-4 represents the amplitude levels of the first seven harmonics.

The amplitude variations corresponding to three levels of flow degradation

(10, 20, and 30 percent) were analyzed by both methods. The baseline

difference and signature difference are shown in Figs. 5-5 and 5-6,

respectively.

Both methods showed a good correlation with a degree of flow degra-

dation at seventh harmonic; however, a good correlation could not be

38

mm . .. . ..... ... 4 1 . ' "

0-

O BASELINE* 10%

41-20%-10- < 30%

-20

D

-

<-30z0

WD -40-

-50-

-60- f 1 '

HARMONIC ORDER (fm)

FIG. 5-4. Wear Vibration mplitude vs Harmonic Order

39

25-

010%<> 20%

20 030

Z 15-wwLi.

0-z0-Jw0

0 0 + 0

S 0 0

1o 2 3 4 5 6 7

HARMONIC ORDER yH

FIG. 5-5. Wear Baseline Difference vs Harmonic Order

40

35

o BASELINE@ 10%420%

30 - 30%

25

wQ 20zw

~150

0 100

z

f50

HARMONIC ORDER N)

FIG. 5-6. Wear Signature Difference vs Harmonic Order

41

., A A -.I!

obtained at lower harmonics. This situation can be endorsed by the fol-

lowing consideration. The acoustic signal which is altered due to the

flow degradation is a leakage flow noise across the component. The

noise created by the leakage flow mainly contains high frequency signa-

tures. Hence, the degree of flow degradation can be better detected at

higher harmonic frequencies.

Bearing Damage

Analysis of bearings using vibration analysis of rotating machinery

has been utilized successfully by industry for some time. Signature

analysis of bearings can provide information concerning the specific lo-

cation and severity of the defect. The procedure utilized requires a

highly trained technician to evaluate and interpret the signature. It

was not the intent of this project to "re-invent the wheel." The scope

of the test was to evaluate the resulting signature from a damaged bear-

ing and see if it could be detected from either of the two methods and

thus require no human interface.

The pumps utilized sealed, roller, non-friction bearings. The

system consisted of seven roller bearings in which one was scored for

test purposes. The vibration amplitudes are shown in Fig. 5-7. The

baseline and signature difference methods are shown in Figs. 5-8 and

5-9, respectively. Since there was only one bearing damage situation

introduced to the test pump, it is not possible to discuss a trend of

the baseline differences; however, the baseline difference itself can be

42

*1 ,, ..

0-

o BASELINE* DAMAGED BEARING

-10-

Lu -20-

-j

< -30-z0

F -4

M 00

50 0

*1 0

0 0

-60- 0 0 -11o 2 3 ~5 67

HARMONIC ORDER (10

FIG. 5-7. Bearing Damage Vibration vs Harmonic Order

43

25

~2O

0is

ccLiUU-

L 0 -

z

0 05-

0 0

fo 1 2 3 4 5 6 7HARMONIC ORDER um)

FIG. 5-8. Bearing Damage Baseline Difference vs Harmonic Order

444

35 - OBASELINE0 DAMAGED BEARING

30-

25

0

u 20

IL

9.-z0

cc 0

0 10

HARMONIC ORDER (H)

FIG. 5-9. Bearing Damage Signature Difference vs Harmonic Order

454

an indication of the damage. The signature difference in Fig. 5-9

shows some promising results at the higher frequencies; namely, the

sixth and seventh harmonics. Due to te characteristics concerning

the construction of the bearing assemblies of hydraulic pumps, they

are replaced and not repaired; thus, the limits set down by an analysis

method concerning bearing damage represent a go/no-go decision con-

cerning the pump's mechanical integrity.

Result Summary

From the analyses of the test results, the capability of the

acoustical diagnostic method can be summarized as shown in Table 5-1.

The signature difference demonstrated a better potential as a non-

intrusive diagnostic method. The analyses of the test results indicate

that the higher frequencies offer important information for the detec-

tion of failures.

Table 5-1. Test Result Summary

Failure Mode Baseline Difference Signature Difference

Cavitation Not applicable Increase at 6th and7th harmonics

Wear Increase at 7th Increase at 7th(Flow Degradation) harmonic harmonic

Bearing Damage Increase at all Increase at 6th andharmonics 7th harmonics

46

Further Investigation

Cavitation can be related to the "popping" associated with bubble

collapse, which can be considered a random high frequency phenomena. Wear

experienced by a pump is related to the leakage or backflow corresponding

to the increased clearances between the contacting surfaces. This leakage

contributes a high frequency characteristic to the pump's overall vibra-

tion signature. The significance of the higher frequencies lead to an

investigative test. The initial testing considered of analyzing a fre-

quency range from 0-2 kHz. The frequency range was expended to 20 kflz on

a hydraulic vane pump operating with a damaged vane. The resulting

frequency spectrum as seen on the spectrum analyzer is shown in Fig. 5-10.

Several peaks can be observed on the spectrum. Generally, increasing

the frequency range decreases the resolution capability of the analysis;

however, commercially available analyzers, through translation techniques,

maintain the necessary resolution at the expense of increasing the analy-

at 10550 Hz in Fig. 5-10 is analyzed in Fig. 5-11. This method illus-

trates the capability of investigating higher frequencies as a potential

diagnostic method. The methods applied at the lower frequencies consis-

ted of harmonic analysis. When analyzing higher frequencies, waveform

analysis, such as RMS power summations over a specified range of frequen-

cies, could prove to be a very powerful diagnostic tool. The higher

frequencies will be of major concern when analyzing the frequency char-

acteristics of non-rotating components such as valves and cylinders.

47__ __A

FIG. 5-lu. Vane Pump Freauercy Spectruni

I'2 I-1. Vwinf P'2[ FCa(,i, U V ectruo-Trans1,ated

Accelerometers usually have upper frequency ranges in the order of

40 kHz; however, some piezoelectric devices can measure:frequencies in

the order of 100 kHz. The higher frequencies combined with various sig-

nature analysis techniques may be the key to the development of a complete

diagnostic analysis system.

The development of a non-intrusive diagnostic method would consist

of an analysis technique which would involve a minimal amount of human

interface for the diagnostic evaluation of the vibration signature. The

diagnostic method to be utilized including frequency range and the wave-

form analysis technique would be part of a dedicated software program

used in a microprocessor spectrum analyzer. Fig. 5-12 illustrates a

flow chart that would accompany the signature difference analysis method

used in Figs. 5-3, 5-6, and 5-9. A large transition exists from the test

results of the project and Fig. 5-12; however, this serves to illustrate

the ideology behind the proposed diagnostic method. The parameters to

be entered into the analysis program would consist of values of the sig-

nature difference and corresponding harmonics which would set vibrational

setpoints from which to compare the vibrational amplitudes of hydraulic

components in service. The setpoints would represent limit values in

relation to the incoming signal for values of wear, cavitation, or damaged

bearings.

A complete diagnostic system would consist of several such sub-

routines corresponding to various failure modes and the types of component

under test. P

49________1

LINITALJZE A/D PORT AS MIT

DIGTME TRANSDUCER SIGNAL

FOURIER TRANSFORMTO

FIG. 5-12.BL Logc Char

SIGNTUR DIFERECE S = A f,-A 14

50

SE 04F- VAUS(SI AVTT.

WEARAND EARIG, CRRESONDITO SPCIFID HAMONI

CHAPTER VI

CONCLUSIONS AND RECOMMENDATIONS

The following conclusions can be drawn from the results of the

project:

1. Transducer verification tests were completed comparing micro-

phone and accelerometer methods to be used as a non-intrusive

diagnostic tool. Both methods produced distinguishable dif-

ferences in their signatures corresponding to operating con-

ditions of cavitation and vane damage.

2. The structureborne noise was selected for use in further

development of the diagnostic method because its test results

showed better consistency on all harmonics and it has fewer

environmental limitations.

3. Cavitation can be detected by the signature difference analysis

method. The degree of cavitation severity was best indicated

by 6th and 7th harmonics.

4. Wear damage which leads to the flow degradation can be detected

by both the baseline and signature differences. The 7th har-

monic gave information on wear severity.

5. Bearing damage of the test vane pump can be found by increases

in the 6th and 7th harmonics of the signature difference.

6. It was found as a result of the tests that higher frequencies

give important information to detect failures on hydraulic

components.

51___1

- - - .4_',.•.--

The following recommendations are made:

1. The program is in the early stage of development; therefore,

other analysis techniques should be investigated.

2. The frequency range of investigation should be expanded to

account for the high frequency contributions. For example,

the frequency range of 0-100 kHz should be investigated utiliz-

ing various analysis techniques to define the most accurate di-

agnostic technique.

3. Testing should investigate the effect on the vibration signature

in response to small and large variations in the system's oper-

ating parameters of temperature, pressure, aeration level, speed,

and level of contamination.

4. Investigation and verification tests will be necessary for the

diagnostic method to detect two or three different types of

failures occuring at the same time.

52

• _ . , . i .- _..

REFERENCES

1. Totty, C., and R. Inoue, "Non-Intrusive Diagnostic Methods for

Fluid Power Systems," The BFPR Journal, 1981, pp. 399-403.

2. Maroney, G. E., "Acoustical Signature Analysis of High Pressure

Fluid Pumping Phenomena," Doctoral Dissertation, Oklahoma State

University, Stillwater, Okla., 1976.

3. Iwanaga, M., and K. H. Tsai, "Hydraulic Reservoir Design-Part 1:

Sloped Screen Configuration," The BFPR Journal, 1980, pp. 209-215.

4. Nipper, M. A., "Adapting Commercially Available Computer for

Process Control," The BFPR Journal, 1981, pp. 393-398.

53

APPENDIX A

DETAILS OF PUMP BREAK-IN

The break-in procedure utilized in the project followed the manufac-

turer's guidelines.

The high wear rate during the break-in period is partially due to

surface roughness being worn from the original profile of the internal

interfaces of the pump. The pressure increments during the break-in

period are to gradually load the pump, resulting in a more uniform wear

of the internal interfaces. A test was run to verify a constant baseline

signature of the pump prior to break-in. This was important for pur-

poses of comparing the data as in the baseline index. Similarities in

the baseline signature are important. A test was run to verify the in-

formation of the baseline signature during break-in and to evaluate the

manufacturer's proposed break-in procedure.

Break-In Evaluation

Background

Since break-in periods are associated with high wear rates, ferro-

graphic oil analyses were conducted at regular intervals during the break-

in period. A correlation was made between the ferrographic density

readings and the formation of the pump's baseline signature. The anti-

cipated results would yield a simultaneous decrease in the amount of

wear particles exhibited from the ferrographic analysis, as the pump

signature stabilized.

54

4

Break-In Procedure

1. Operate the pump at the manufacturer's recommended operating

conditions during break-in.

2. Take ferrographic oil samples every 5 minutes throughout the

durat: of the break-in period.

3. Record the vibration signature at 15-min intervals correspond-

ing to the pressure increase associated with the break-in

period.

Analysis

The overall root mean square (RMS) value of sound pressure levels

was evaluated from 0-2 kHz including the first seven harmonics of the

fundamental vane pass frequency. The RMS value corresponding to each

pressure interval was divided by the RMS of the baseline signature,

as developed after 3 hours of operation. The results are plotted in

Fig. A-i. It can be seen that the formation of the baseline is approxi-

mately complete following 45 minutes of operation. The results of the

ferrographic analysis are plotted in Fig. A-2. The ferrographic

analysis provides information concerning the amount of wear particles

contained in a given oil sample. The figure indicates that the particle

density decreased rapidly through the first 15 minutes of operation.

It continued to decline to a steady value throughout approximately

45 minutes of operation. There is good correlation between Figs. A-1

and A-2, indicating the wear associated with break-in is complete

after 45 minutes of operation. This is consistent with the analysis of

the vibration signature.

55

- Z- L.. .-

2.0-

1.75-

1.50-

125-

z 1.0 00

75-

50-

25-

O ;5

PECENT-RATED PRESSURE

FIG. A-i. Non-Intrusive Diagnostics Break-In Procedure

56

ci

wL

0-zwI

*Y I

0.00

S_

/ a)

/C

0 O) CMJ

31dV4YS :10 WMNKWMV~ AJ9N3a rfix~ouui

57

Summary

The analysis verified the manufacturer's break-in procedure. The

break-in procedure was utilized throughout the project for establishing

the baseline signature for each pump.

It is recommended in the development of a non-intrusive diagnostic

technique that the effect of various break-in procedures on the result-

ing baseline signature of a hydraulic pump be evaluated.

58

.... 4 . .

APPENDIX B

DIAGNOSTIC TEST PROCEDURES AND OPERATING CONDITION

Test Procedures

Each test consisted of Basic Operating Procedures. These procedures

were to insure consistent operating conditions which could be repeated

for any given test.

Basic Operating Procedures for Tests:

1. Each pump which was disassembled to implant defective components

was reassembled to the factory specified torque. Each pump was

mounted on the test block with a torque of 50 NM to insure that

*the structural vibration was consistent throughout each test.

2. Each pump was subjected to the break-in procedure as set down by

the manufacturer for the particular pump.

3. Preceding break-in, the test operating conditions of temperature

and pressure were maintained at steady state for 1.0 hour, prior

to the acquisition of the baseline signature.

4. Prior to the data acquisition of any given test, the system

aeration level was measured. The level was kept at less than

1.0 percent except during cavitation tests.

5. The instrumentation was subjected to a warmup period of no less

than 45 minutes prior to each test.

6. The transducers were calibrated according the manufacturer's

procedures.

59

!I*

TEST OPERATION CONDITIONS

CAVITATION TEST Number TH-DVT-002

Shaft Speed 1200 RPM

Pump Inlet Pressure 6.0 PSIG

Pump Discharge Pressure 2250 PSIG

Hydraulic Fluid MIL-L-2104

Fluid Temperature 150OF

Flow Rate 6.4 GPM

Aeration Level Controlled to maintain specif-ic cavitation severities

WEAR TEST Number TH-WCT-005

Shaft Speed 1200 RPM

Pump Inlet Pressure 6.0 PSIG

Pump Discharge Pressure 2250 PSIG

Hydraulic Fluid MIL-L-2104

Fluid Temperature 150°F

Flow Rate 6.2 GPM

Aeration Level less than 1.0%

DAMAGED BEARING TEST Number TH-BND-006

Shaft Speed 1200 RPM

Pump Inlet Pressure 6.0 PSIG

Pump Discharge Pressure 2250 PSIG

Hydraulic Fluid MIL-L-'2104

Fluid Temperature 150 °F

Flow Rate 6.3 GPM

Aeration Level less than 1.0%

60

- -- "--- - -. - - , l

!+- .:.--.-. . . ++,. .. .....= . . ... .... .,,.,.' L ,... .. . - s +.-

APPENDIX C

TEST FACILITY

The acoustic facility at the Fluid Power Research Center was devel-

oped to meet the test requirements throughout all phases of the project.

The test system was designed to facilitate all phases of a testing pro-

gram towards the development of a non-intrusive diagnostic field package.

The layout of the facility, which occupies 1400 sq. ft. of the FPRC, is

shown in Fig. C-1. The facility can be subdivided into three areas: test

cell, reverberant room, and instrumentation lab.

The test cell consists of the primary and secondary fluid condition-

ing system, drive system, and the contaminant sensitivity test stand.

These systems are located outside of the reverberant room so as to not

interfere with the acoustic measurements. The reverberant room is an

acoustically reflective environment which includes the test circuit.

The test circuit accommodates the test components--hydraulic pumps, motor,

and valves. The instrumentation lab contains signature analysis measure-

ment equipment. The computer test stand controller located in the instru-

mentation lab provides full control of all systems during a test. The

entire test, including the data acquisition, is operated from the instru-

mentation lab. The closed circuit T.V. cameras provide visual inspection

of operating equipment during tests.

Primary Fluid Conditioning Test Stand

The primary fluid conditioning test stand, Figs. C-2a and C-2b, was

61

L|

A

__

A) PRIM. FLUID-COND. F) TEST VALVEB) SEC. FLLE>-COND. G) TEST MOTORC) DRIVINJG MOTOR H) LOAD PUMPD) MOUNJTING BLOCK W)FSTRUMENTATIONE) TEST PUMP J) OFFICE

FIG. C-i. Test Facility

62

ccu

00

000

Z (1)

CO M

Q0

CCA

I--

00-S-

IX (

w6

> CO) O

...................................................

FIG. C-2b. Fluid Conditioning Stand

FIG. C-3. Air Injecting and Mixing Vessel

64

constructed during the contract to provide the operating test conditions.

The inlet pressure, discharge pressure, fluid temperature, and aeration

level were maintained to a steady state prior to the recording of data.

The parameters can be controlled both manually or automatically. The

test stand is interfaced into a test stand controller for automatic

monitoring of the operating parameters.

Aeration Levels

The primary fluid conditioning system provided control of the fluid

aeration level. The system consists of aeration (air injection), aeration

measurement, and deaeration (air removal) equipment. The tests, excluding

cavitation, were operated under a constant aeration level. Air injection

is provided through the air injecting vessel and the mixing vessel as

shown in Fig. C-3. Air is injected into the injection chamber to a spec-

ified pressure. The air in the injection chamber is then injected into

the mixing chamber. The amount of air injected into the mixing chamber

is proportional to the pressure drop in the injection chamber based on

the ideal gas equation of state. The air and oil in the mixing chamber,

in predetermined proportions, is then added to the system fluid.

The deaeration system consists of the mixing vessel and the system

reservoir. The system fluid passes through the mixing chamber, which

can be subjected to a vacuum. The slight vacuum in the mixing chamber

acts to withdraw the air from the oil. The reservoir was designed with

air removal capabilities. The reservoir utilized the slope screen method

65

proposed by Iwanaga [3] for air bubble removal. The reservoir is shown

in Fig. C-2b. The reservoir utilizes an inclined wire mesh screen to trap

the air bubbles which are in the fluid. The reservoir is bypassed , ring

aeration. The system provides approximate quantitative monitoring and

control of the fluid aeration level.

The drive system is located in the test cell. It consists of a

250 HP variable speed motor which is coupled to the test pump through

belt drives. The system provides the capability of operating test compo-

nents accurately over a wide range of speed.

The test system utilized in the FPRC pump contamination sensitivity

test was designed to maintain the controlled amount of test contaminants

which were introduced to the test pumps. A schematic of the system is

shown in Fig. C-4. The contaminants were injected to specifications into

the fluid. The system is manually operated and monitors all the operat-

ing test parameters.

The test components were operated in the reverberant room as shown

in Fig. C-5. The test pump was mounted on a cement block to stabilize

the vibration resulting from the drive shaft. The pump is mounted di-

rectly on an aluminum mounting block. The block eliminated the effects

of lateral vibration. The rigidity of the mounting block insured that

the vibration signature from the pump was not a result of outside force

exci tatlons.

66

-i INJECTION CHAMBER

FLOW ONITO

L66

M'

VAV F~.

FIG. C-5 Pump Operation in theReverberent Room

68

-11

The test facility utilized a reverberant room. Reverberant rooms

are acoustically reflective environments which negate the location effect

of the transducer (microphone). The room contained rotating vanes to

break up standing wave patterns within the room. Standing waves create

nodes (sound levels of high intensity) and antinodes (low intensity).

The reverberant room was utilized for the measurement of the total acoustic

power of a source whose sound energy is distributed over a wide band of

frequencies.

The facility provides the necessary equipment and instrumentation

to carry out a wide variety of tests, including both structureborne and

airborne measurements.

69

APPENDIX D

TEST STAND CONTROLLER

The test stand controller shown in Fig. D-1 continuously monitored

testing and maintained all operating conditions to their preset values.

At the onset of each test, the desired operating conditions were entered

into the program as setpoints. Once the setpoints were entered, the com-

puter would bring the test system to a steady state operating condition

corresponding to the preset values. The operating conditions of the

test stand which were monitored by the computer included pump inlet

pressure, fluid temperatures, RPM, and flow rate.

The test controller provided visual inspection of the test pump and

test stand through two T.V. cameras. It provided full control of both

hydraulic and pneumatic systems through operation of 18 solenoid valves.

The software contained emergency shutdown procedures through a continuous

monitoring of the test. The controller had a visual display which was

a continuous record of the test stand's operating status.

A commercially available TRS-80 microcomputer was used for the

test stand controller (4]. The human interface and mass storage blocks

were developed at the FPRC.

Complete technical information including system schematics can be

obtained for the TRS-80, allowing system modification and repairs to be

performed by the system designer. The total cost of the TRS-80 system

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was approximately $750.

The standard (STD) card rack system was selected for the control

interface between the TRS-80 and the vibration diagnostic test system

(VDTS). By obtaining a TRS-80-to-STD bus interface card, the TRS-80 has

full control of the STD bus through a ribbon cable interconnection.

The VDTS has several analog parameters that must be monitored and

controlled. For this purposed, a STD analog-to-digital (A/D) converter

card was obtained. The STD A/D card offers 32 separate input channels

through which pressure and temperature signals can be measured. The addi-

tional input channels add to the expandability of the system.

The computer controller for the VDTS also had to have the capabili-

ties to monitor switch closures, control AC and DC relays, and update an

LED matrix status indicator. A 64-channel STD digital input/output

board was selected to perform these functions.

To facilitate communications between the TRS-80 and a line printer,

a serial data interface card was selected. This card also has the capa-

bilities to allow for modern communication between the TRS-80 and the

University's IBM computer, should this feature be needed in the future.

To allow for simplicity in interfacing the computer to the AC and

DC relays, optically isolated solid state relay racks were used for the

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VDTS. This type of relay rack allows 16 small relay modules to be mounted

on a printed circuit board strip. The printed circuit board is then ter-

minated with an edge connector containing all the control lines for each

relay. By supplying digital control signals to the edge connector, con-

trol of AC voltages of up to 220 V and DC voltages of up to 80 V is eas-

ily implemented.

Interaction between the computer and the operator is implemented

using several different components. The graphics capabilities of the TRS-

80 CRT will be used to display a schematic of the fluid conditioning sys-

tem and display the status of all the components during the test. Also,

an LED status display was developed using bi-colored LED's. Each LED

represents a certain temperature or pressure and the status of that param-

eter; green for normal, red for marginal, blinking red for critical or

failure. A printer provided hard copy containing the values of the test

operating conditions, pressure, temperature, etc. LED's are also used

to indicate the status of relay closure solenoids.

Diagnostic Hardware and Software Development for Field Application

The completion of the microprocessor test stand controller was the

first stage of a program devised to develop the necessary hardware for a

diagnostic system. The development program of the microprocessor test

stand controller was two-fold: 1) The complete monitoring and control

of the setpoints for a given test; i.e. inlet pressure, temperature,

etc. 2) The complete data acquisition consisting of collection, reduc-

tion, and analysis. The test stand controller was designed with an

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upward expandability towards the development of both the hardware and

software for a dedicated field unit.

The test stand control unit was built with four major system

modules in mind-system microprocessor, control and data acquisition,

program storage, and human interface.

The use of a standard (STD) bus for the control interface of the

test stand controller provides the upward capability towards a stand

along diagnostic analysis unit. The test stand controller provided

information concerning hardware capabilities of the microprocessor. With

the fundamentals in hand, the next stage of data processing and analysis

can be interacted into the capabilities of the test stand controller.

The diagnostic system development would consist of using the microcom-

puter on the test stand controller. The test stand controller uses a

commercially available microcomputer. Upon completion of the appropriate

software, the transition to a dedicated field diagnostic unit would con-

sist of replacing the microcmputer with a STD-bus-based Z80 microproces-

sor card. The developed software prototype on the microcomputer could be

loaded into a nonvolatile type memory and installed in the STD bus.

Instrumentation

The instrumentation utilized in this project is illustrated in Figs.

D-2 and D-3. The system represents the functions of signal transduction,

conversion, analysis, and display. An accelerometer was the transduction

device measuring the structural vibration of the test component. The

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FIG. D-2. Milcrocomputer Test Control System

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FIG. D-3. Test Analysis System

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charge amplifier was utilized to amplify the electrical waveform from

the transducer. The passband filter was utilized to filter out the fre-

*quencies within the signature outside of the desired analysis range

The oscilloscope had the capability to digitize and store the real time

signature on a floppy disc. The oscilloscope offers the capability of

storing data in a digitized form which can be downloaded to a computer

for further analysis. This gives the facility the capability of collect-

ing data accurately which can be analyzed by a computer at a later time.

This enhances the analysis capability of the data, for correlations of

data can be manipulated through any software reduction programs which

may be of interest.

The data reduction of the vibration signature Is analyzed on a

spectrum analyzer. The data are subsequently acquired, transformed, and

stored in memory of the spectrum analyzer. The storage capability of

the analyzer provided the comparison of a pump's baseline signature to

a corresponding operating condition. The continuous improvements in the

technology of spectrum analyzers will broaden the research capabilities

in the area of vibration signature analysis.

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